Papermaking machines removing water from raw material of paper are generally provided with a wire part, a press part, and a dryer part. The wire part, the press part, and the dryer part are arranged in this order in a direction in which a wet paper web is conveyed.
The wet paper web transferred from the wire part to the press part is conveyed usually by a felt including batt layers needled onto a base fabric and then pressed together with the felt by a roll press or a shoe press mechanism to remove water inside the wet paper web.
The felt is generally formed by intertwining and integrating a batt fiber with the base fabric by needling. The base fabric used is generally a woven fabric woven by a weaving machine. As methods for producing a woven fabric, there are hollow weaving and plain weaving. The hollow weaving is a method in which warp yarns on a weaving machine (warping yarns, which are weft yarns of felt (CMD yarns: Cross-Machine-Direction yarns)) and weft yarns on the weaving machine (interwoven yarns, which are warp yarns of the felt (MD yarns: Machine-Direction yarns)) are woven in a loop shape (in an endless shape) in advance. In addition, plain weaving is a method in which warp yarns on a weaving machine (warping yarns, which are warp yarns of felt (MD yarns: Machine-Direction yarns)) and weft yarns on the weaving machine (woven yarns, which are weft yarns of the felt (CMD yarns: Cross-Machine-Direction yarns)) are woven up into a woven fabric in such a manner that the length of a warp yarn direction of the woven fabric is equal to the length of a running direction of the felt in a papermaking machine. In this method, both ends of the woven fabric woven up are bonded together (sewed together) to form the woven fabric into a loop shape (for convenience, hereinafter, warp yarn and weft yarn, respectively, are referred to as warp yarn (MD yarn) and weft yarn (CMD yarn), respectively, of felt.
Functions required for the felt include equalizing a pressure state under pressurization by a press so as to smooth the surface of a wet paper web without causing marking on the surface thereof and uniformly squeeze water out from the wet paper web without crushing the wet paper web. In addition, the functions required for the felt also include reducing time from setting of a felt in a papermaking machine and starting of use of the felt to reaching a normal operation speed, namely an attunement time, and stabilizing running.
In Patent Literature 1, in order to simultaneously suppress both a stripe-like marking in a warp yarn direction and a stripe-like marking in a weft yarn direction to further improve surface properties of paper, there has been disclosed a felt using a base fabric composed of a woven fabric that has a double warp-single weft texture structure consisting of an upper warp yarn on a paper surface side of the fabric, a lower warp yarn on a running surface side thereof, and weft yarns interwoven by double weaving so as to be intertwined with both the upper and the lower yarns, in which the upper yarn is interwoven in a higher density than the lower warp yarn. In the base fabric, the upper warp yarn is composed of a soft twist yarn of a plurality of filaments softly twisted so as to be flattenable and the weft yarns are interwoven such that knuckle portions in each of which the weft yarns bend in such a manner as to pass along the upper side of only one upper piece of the upper yarn are arranged at an equal interval corresponding to three or more upper yarns.
In Patent Literature 2, in order to provide a press felt that does not cause any marking nor crush, there has been disclosed a felt using a base fabric composed of a set of top-side MD yarns, a set of bottom-side MD yarns, and a set of CMD yarns interwoven with the top-side MD yarns and the bottom-side MD yarns. In the base fabric, the top-side MD yarns, the bottom-side MD yarns, and the CMD yarns are interwoven in a series of repeating units in which each of the top-side MD yarns forms a long MD paper-side float yarn above specific consecutive plural ones of the set of CMD yarns.
Patent Literature 3 has disclosed a papermaking felt in which the number of pieces of MD yarns on the upper surface of a base fabric is twice the number of pieces of MD yarns on the lower surface thereof in order to provide a woven fabric having a high vibration absorbing capacity used in papermaking machines so as to provide a felt having high elasticity and resilience to assure better runnability, fewer maintenance stops, and improved paper quality.